#!/usr/bin/env python3
# -*- coding: utf-8 -*-

def binary_search(list, item):
    low = 0
    high = len(list) - 1
    while low <= high:
        mid = int((low+high)/2)
        guess = list[mid]
        if guess == item:
            return mid
        elif guess > item:
            high = mid - 1
        elif guess < item:
            low = mid + 1
    return None

my_list = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

print(binary_search(my_list, 5))
print(binary_search(my_list, 15))